I've been in that position once early on in my career - single developer bearing the load of a project that should have been the work of 3-4 people. It didn't end well - I got the thing done but performance, quality etc were way below par and I got away from the project and company as fast as I could. Nowadays with more experience (not just technical) I would have seen the shit show coming a mile off.

The key factor here was that management dictated a timetable then pulled a fast one and decided to pre-release with a "soft launch" three-quarters of the way through. It was insanity, and older-me would have quit on the spot and told them where to stick it where the sun didn't shine. As it was I got something out the door more or less on time, but it was absolutely nothing else to be proud of.

My advice to younger-me and junior developers in general is that management are generally clueless about software development, even if they did it once in the past (hello Elon Musk) and part of your job is to push back against unrealistic deadlines and features and if you don't do that, you are doing yourself and your company a disservice. Don't let hubris and fear get the better of you.